11
ATC OPERATION
ATC Functional Overview
Just as ABS improves vehicle stability during braking,
ATC improves vehicle stability and traction during vehicle
acceleration. The Bendix EC-60 controller ATC function
uses the same wheel speed information and modulator
control as the ABS function. The Bendix EC-60 controller
detects excessive drive wheel speed, compares the speed
to the front, non-driven wheels, and reacts to help bring the
wheel spin under control. The controller can be configured
to use engine torque limiting and/or differential braking to
control wheel spin. For optimal ATC performance, both
methods are recommended.
ATC/ESP Lamp Output/ATC Mud/Snow Switch
Input
Advanced ECUs control the ATC/ESP dash lamp as
follows.
The ATC/ESP dash lamp illuminates:
1. During power up (e.g. when the vehicle is started) for
approximately 2.5 seconds and turns off after the self
test is completed, providing no diagnostic trouble codes
are present.
2. When ESP or ATC is disabled for any reason.
3. During an ESP or ATC event (the lamp will flash rapidly
at a rate of 2.5 times per second).
4. When the ECU is placed in the ATC off-road mode
(the lamp will flash steadily at a rate of once per 2.5
seconds). This notifies the vehicle operator that the
ATC Mud/Snow mode is active.
5. When the ECU is placed in the ABS off-road mode.
When in this mode, ESP will be disabled below 25 mph
and its inactive status will be indicated by a steadily
illuminated ATC/ESP lamp.
Differential Braking
Differential braking within ATC is automatically activated
when drive wheel(s) on one side of the vehicle are spinning
excessively, which typically occurs on road surfaces
with patches of ice. The traction system will then lightly
apply the brake to the drive wheel(s) that are spinning
excessively. The vehicle differential will then drive the
wheels on the other side of the vehicle.
Differential braking (as part of ATC functionality) is available
at vehicle speeds up to 25 MPH.
Disabling ATC Differential Braking
ATC differential braking is disabled under the following
conditions:
1. During power up (e.g. when the vehicle is started), until
the ECU detects a service brake application.
2. If the ECU receives a J1939 message indicating that
the vehicle is parked.
3. When the dynamometer test mode is active. The
dynamometer test mode is entered using the diagnostic
blink code switch or by using a diagnostic tool (such as
Bendix
®
ACom
®
Diagnostics).
4. In response to a serial communications request from
a diagnostic tool.
5. If ATC Differential Braking function is activated for a long
time period to avoid overheating of the brakes. It would
take approximately 3 continuous minutes of activation
for the timeout to occur. Once timed out, approixmately
2 minutes of "cool off" time would be required before
ATC Differential Braking can be used again.
6. When certain diagnostic trouble code conditions are
detected.
Engine Torque Limiting with Smart ATC
™
Traction Control
The Bendix EC-60 controller uses Engine Torque Limiting
to control drive axle wheel slip. This is communicated to
the engine control module (using J1939), and is available
at all vehicle speeds.
Bendix
®
Smart ATC
™
Traction Control
The Bendix EC-60 controller has an additional feature
known as Smart ATC
™
traction control. Smart ATC
™
traction control monitors the accelerator pedal position
(using J1939) to help provide optimum traction and vehicle
stability. By determining the driver’s throttle input and
adapting the target slip of the drive wheels to the driving
situation, the Smart ATC
™
traction control allows higher
wheel slip when the accelerator pedal is applied above a
preset level.
The wheel slip allowed by Smart ATC
™
is decreased when
driving through a curve for improved stability.
Disabling ATC Engine Control and Smart ATC
™
Traction Control
ATC Engine Control and Smart ATC
™
traction control will
be disabled under the following conditions:
1. In response to a serial communications request from
an off-board tool.
2. At power-up until the ECU detects a service brake
application.
3. If the ECU receives a J1939 message indicating that
the vehicle is parked.
4. If the dynamometer test mode is active. This may be
accomplished via an off-board tool or the diagnostic
blink code switch.
5. When certain diagnostic trouble code conditions are
detected.
